As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased. Among such secondary batteries is a lithium secondary battery exhibiting high energy density and operating voltage and excellent charge retention and service-life characteristics, which has been widely used as an energy source for various electronic products as well as various kinds of mobile devices.
Depending upon types of external devices in which secondary batteries are used, the secondary batteries may be configured to have a detachable type structure in which the secondary batteries can be easily inserted into and removed from the external devices or to have an embedded type structure in which the secondary batteries are embedded in the external devices. For example, it is possible for a user to insert or remove a battery into or from a device, such as a laptop computer, as needed. On the other hand, devices, such as specific mobile phones, require an embedded type battery pack due to the structure and capacity thereof.
Meanwhile, various kinds of combustible materials are contained in the lithium secondary battery. As a result, the lithium secondary battery may be heated or explode due to the overcharge of the battery, the overcurrent in the battery, or other external physical impact against the battery. That is, the safety of the lithium secondary battery is very low. For this reason, safety elements, such as a positive temperature coefficient (PTC) element and a protection circuit module (PCM), which are capable of effectively controlling an abnormal state of the lithium secondary battery, such as the overcharge of the lithium secondary battery or the overcurrent in the lithium secondary battery, are connected to a battery cell of the lithium secondary battery.
In general, an embedded type secondary battery pack uses a plate-shaped battery cell, which is suitable for electrical connection, and a PCM is connected to the battery cell via conductive nickel plates by welding or soldering. That is, the nickel plates are connected to electrode terminals of the battery cell by welding or soldering, a protection circuit board (PCB) is connected to one side of each of the nickel plates by welding, a protective tape is attached to the other side of each of the nickel plates, and electrode tabs of the PCB and the nickel plates are connected to each other by welding in a state in which the PCB is in tight contact with the battery cell. In this way, the PCM is connected to the battery cell to manufacture a battery pack.
A conventional PCM case includes an upper case and a lower case. That is, the PCM case is a two-unit member. The upper case is coupled to the lower case in a state in which the PCM and the safety elements are loaded in the lower case.
It is required for the safety elements, including the PCM, to be maintained in electrical connection with the electrode terminals of the battery cell and, at the same time, to be electrically isolated from other parts of the battery cell.
To this end, insulative tapes are attached to various members, including the PCM. In addition, a portion of a sealed part of a battery case, in which the battery cell is received, is bent, and an insulative tape is attached thereto or a barcode is printed thereon. That is, the process is very complicated.
Since a plurality of insulative tapes or parts is required to achieve safe connection as described above, a battery pack assembly process is complicated and manufacturing cost is increased.
In addition, when external impact is applied to the battery pack, the PCM may be damaged or dimensional stability of the battery pack may be greatly lowered due to the use of the insulative tapes, which exhibit low mechanical strength.
Therefore, there is a high necessity for technology that is capable of reducing the number of members mounted at the battery cell to simplify an assembly process, achieving stable coupling between members loaded on the battery cell, and protecting the PCM.